R1 Ch3 R2 H

FIGURE 4.17 Anisatin-type sesquiterpenes (compounds 109-117)

As shown in Scheme 4.9, base treatment of pseudoanisatin (118) led to the formation of the Y-lactone 118a with the inversion at C-4. Pseudomajucin (148) and its 7-0-0-D-glucoside (149), which were isolated from the pericarps of I. majus (Kouno et al., 1989), were found to consist of the same carbon skeleton as that of 118a. The structure of 148 was established by x-ray crystallo-graphic analysis. The glucoside linkage position in 149 was determined as C-7 by glycosylation shift (2.6 ppm) at C-7 compared with that of 148. No pseudomajucin-type has so far been known as a natural product except 148 and 149 (Figure 4.22).

In 1999, new cycloparvifloralone-type sesquiterpenes were found (Figure 4.23). Cycloparvi-floralone (150) occurred in the leaves of I. parviflorum, and (11)7,14-ortholactone of 14-hydroxy-3-oxofloridanolide (151) was isolated from the fruits of I. floridanum (Schmidt et al., 1999), whereas I. merrillianum produced merrillianone (152) (Huang et al., 1999). All of these sesquiterpenes possess a hitherto rare ring system with a cage-like acetal and hemiacetal structure.

New carbon skeletal sesquiterpenes, which are not able to take their place with the known subclasses of Illicium sesquiterpenes, have been found as natural products, as shown in Figure 4.24. Anislactones A (153) and B (154) were isolated from the fruits of I. anisatum (Kouno et al., 1990). The structure of anislactone A was established by an x-ray crystallographic analysis (Kouno et al., 1989), whereas anislactone B was an epimer with regard to the 7-hydroxyl group. Both compounds have unique types of carbon-skeleton that have never been recorded as natural compounds.

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